An analysis of forces and conditions
which influence the successful passage
of a carriage over an intermediate support jack
during downhill multi-span logging

Abstract:

In this paper, a catenary analysis of static skyline, mainline
and haulback cable tensions just prior to an unsuccessful attempt by
a carriage to pass an intermediate support jack is presented. Field
tests were conducted for a range of skyline deflections and span
chord slopes. Data collected during the field tests included static
and dynamic cable tensions and cable geometry. The relationship
between upper span skyline deflection, the percent change in span
chord slopes, and their influence on successful carriage passage was
determined. During the field tests it was observed that maintaining
a taut haulback as the carriage passed the support jack prevented the
carriage from surging out of control and reduced dynamic tension
fluctuations. It was also observed that yarding the loaded carriage
uphill over the support jack was prohibited by skyline deflections
which still allowed successful carriage passage for the downhill
yarding configuration.